The extracellular matrix (ECM) is a complex organization of structural proteins such as collagens and proteoglycans. A wide variety of tissue engineering scaffolds have been created in attempts to mimic features of the native ECM. Notably, microstructural features [1-3], mechanical properties [4-6], and inclusion of soluble or insoluble biomolecules [7, 8] have all been shown to significantly influence cell behaviors such as adhesion, growth, and differentiation as well as to affect material bioactivity for in vivo applications. Heterogeneous tissues with spatially and temporally modulated properties and their biomaterial mimics play an important role in organism physiology and regenerative medicine [9, 10]. An example of particular relevance is the graded interfacial region found between bone and tendon in the musculoskeletal system, which contains complex compositional, microstructural, and mechanical patterns; the gradient interface reduces formation of interfacial stress concentrations that can lead to interface failure while maintaining distinct tendon and osseous compartments [11, 12].
With the understanding that the microstructure, mechanics, and composition of the ECM is dynamic and often spatially patterned or heterogeneous over the length-scale of traditional biomaterials, there has recently been significant effort aimed at moving away from static, monolithic biomaterials towards instructive biomaterials that provide specialized cell behavioral cues in spatially and temporally defined manners [13, 14]. These materials hypothetically recapitulate aspects of the dynamic and spatially heterogeneous constellation of cues presented by the ECM.
The development of molecularly general approaches to spatially control the presentation of multiple biomolecules within porous scaffolds is an important goal for creating advanced biomaterials. Many adhesion ligands, growth factors, and other biomolecules are typically sequestered as opposed to freely soluble within the ECM [28]. Biomolecule immobilization has further shown benefits relative to bolus or even controlled delivery of soluble growth factors [7]; explanations include extended biomolecule half-life, elimination of diffusive dilution [7], and avoidance of cellular uptake that limits long-term bioactivity. While a number of methods have been developed for creating spatial patterns of surface-immobilized biomolecules on 2D surfaces [16, 29-31, 32], many of these approaches are not amenable to patterning within porous scaffolds where conformal contact and/or confinement of fluid flow cannot be readily achieved.
A current limitation in biomaterials science is the lack of universal methods for creating multicomponent, overlapping patterns or gradients of biomolecules within a biomaterial with spatial and temporal control over presented surface densities.
Simple, yet generic tethering chemistries that enable spatial localization of wide range of biomolecules as well as exogenously or endogenously cued release of biomolecules onto a 3D scaffold from clinically relevant biomaterials are needed in the art. Current techniques do not currently exist to effectively separate biomaterial fabrication and spatially-controlled patterning of biomolecules in a manner that is applicable to the wide range of biochemical moieties in the native ECM.